The invention relates to an apparatus for examining the mouths of bottles or the like of transparent material, in which a camera device is disposed on the axis of the bottle to be examined to take photographs of the mouth in order to detect defects, the apparatus also having a light source and at least a first light-conducting member which has a coaxial viewing opening and a first light exit surface to illuminate the mouth.
A known apparatus of this kind (U.S. Pat. No. 4,731,649) has a light-conducting member in the form of a translucent plate above which there are disposed a plurality of stroboscope lamps. Secured to the underside of the translucent plate are two prisms which direct light from the side inwards and obliquely upwards onto the rim of the mouth so that the camera device can take a video picture through the viewing opening in the translucent plate. The prisms are arranged at each side of a channel through which the mouth of the bottle to be examined is moved. In this case, the viewing opening is an oval opening and the translucent plate must supply additional light to illuminate the mouth from the front and rear because the prisms can only illuminate the mouth from the side. It is true that the viewing opening may also be circular but in either case it is impossible with the known apparatus to examine the upper end face of the mouth of the bottle, that is to say the lip in the case of a crown cork bottle. Since the mouth is only illuminated laterally in the known apparatus, the video camera can also only take a kind of collective picture which may contain numerous defects which are anywhere in the material of the bottle mouth or on the side thereof but not on the surface of the lip. The known apparatus is therefore more suitable for examining the mouths of bottles in a bottle manufacturing plant rather than in a bottling plant where work is carried on with considerably higher throughputs of bottles and defects which may impair the fluid-tightness of a bottle, particularly of a bottle to be refilled, are mainly of interest. In addition, the known apparatus works inaccurately because a uniform circular illumination is not possible with it. The illumination of the front and back of the mouth must necessarily be a compromise since the mouth is to be taken through between the prisms. In the known apparatus, this compromise can be accepted because the defects which are mainly of interest are those present in the screw thread on the bottle or in the mouth portion below the lip and are not easily visible looking in the direction along the axis of the bottle.